This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
The offer which by acceptance can become an agreement, as the term is used in law, must possess certain qualities differentiating it from the general class of offers commonly so called. It must purport to create liabilities which are legally enforceable. Thus it is often said that offers purely social or religious in their nature can not form the basis of a contract even if all the other elements are present.1 Cases of this sort can be explained at the common law on the theory that they lack consideration. The same problem exists at civil law and it can not be thus explained. Probably the true explanation is that no liability is intended by either. The same offer might, under different circumstances, amount to a social invitation from a friend or to a contract to furnish food, music and the like for which payment of at least reasonable compensation was to be made; and the intention not to incur legal obligation is the very thing that makes the agreement lacking in consideration.